EPA must designate areas as meeting (attainment) or not meeting (nonattainment) the standard. The
Clean Air Act (CAA) requires states to develop a general plan to attain and maintain the NAAQS in
all areas of the country and a specific plan to attain the standards for each area designated
nonattainment for a NAAQS. These plans, known as State Implementation Plans or SIPs, are developed
by state and local air quality management agencies and submitted to EPA for approval.

The SIPs serve two main purposes:

Demonstrate that the state has the basic air quality management program components in place to
implement a new or revised NAAQS.

Identify the emissions control requirements the state will rely upon to attain and/or maintain
the primary and secondary NAAQS

Each state's SIP must contain a number of elements required by the Clean Air Act, and must be
developed and adopted through a process allowing public input. Once adopted by the state, each
required SIP element must be submitted by the Governor's designee to EPA. EPA must review and act
to approve or disapprove each element.

The SIPs are designed to prevent air quality deterioration for areas that are in attainment with
the NAAQS and to reduce common or criteria pollutants emitted in nonattainment areas to levels that
will achieve compliance with the NAAQS. As the NAAQS change, states must submit revisions to the SIP
to demonstrate attainment and maintenance of those new or revised NAAQS and to meet other statutory
requirements.

The general plan requirements for each nonattainment area are specified in subpart 1 of the Clean
Air Act Part D. The additional provisions for each respective NAAQS are specified in subpart 2 to
subpart 5.

Congress recognized in the 1990 CAA Amendments that the more densely populated Northeast states
share the same airshed, as well as emissions sources and commuting patterns. In order to regionally
address air quality in the Northeast, they created an area from Maine to Northern Virginia, calling
it the Ozone Transport Region (OTR). States in the OTR are required to implement additional control
measures that apply across the region, whether an area in the OTR is attainment or
nonattainment. Learn more about SIP requirements for states in the
Ozone Transport Region.